For some of us, watching online videos provides a break from work. For Kevin Allocca, it is his work. Allocca is the head of YouTube's culture and trends division. He spends his days contemplating, say, cat videos and what makes them go viral. NPR's Neda Ulaby spoke with Allocca about his new book "Videocracy."

NEDA ULABY, BYLINE: Yes, it's a book about surfing the Internet. Kevin Allocca admits this project was partly an excuse to go back and interview the creators of some of his favorite viral videos.

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ULABY: From the Nyan Cat, a sensation in 2011, to Hitler ranting, to that stoned-sounding guy who saw a double rainbow.

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PAUL VASQUEZ: Whoa, oh, my God. Oh, my God.

ULABY: And others whose videos Kevin Allocca especially loved.

KEVIN ALLOCCA: I talked to this guy in upstate New York who puts a red, hot nickel ball on things.

ULABY: A red, hot metal ball that melts through things like a massive block of Velveeta. It got millions of views. So many of these super successful videos raise the question, why?

ALLOCCA: I think that's kind of the story of why I wanted to write this book in the first place is that I think so many things we see, we're like, why?

ULABY: Allocca breaks down the human condition, as performed on YouTube, into a comprehensive taxonomy - reaction videos, remixes, supercuts, pranks, fails and a kind of video Allocca dubs oddly satisfying.

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ULABY: It turns out there are multiple genres of YouTube videos that are just ears getting cleaned. Millions of people find these videos soothing. And they make no sense in terms of conventional media or advertising. Allocca says if what's trending on YouTube tells us something about society, consider one of last year's biggest sensations.

ALLOCCA: Slime.

ULABY: Do-it-yourself make your own slime videos.

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UNIDENTIFIED WOMAN: I'm going to make black slime before I add my powder.

ALLOCCA: And it was the biggest do-it-yourself trend of last year, I would say, in terms of the things that people were creating online - billions of views on these videos.

ULABY: They even created a national shortage of glue. Allocca says we're living in the least predictable, most confounding era in the history of human expression. Viral videos, he says, have become less accidental, more commercialized and YouTube is struggling with how to deal with unsavory, even hateful videos. Allocca says he did not write this book specifically to promote his employer.

But, he says, viral videos serve a valuable social function in a fractured media universe. They give us something to share.

ALLOCCA: We want to be connected to each other and to moments through content. And I think that's sort of what's at the heart of why so many people are successful online is that they create experiences that build community or that build a sense of belonging like, you know, the elevator videos.

ULABY: Elevator videos?

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UNIDENTIFIED MAN: Ten is as high as you can go in any of these elevators.

ULABY: An online community of elevator aficionados give each other's videos hundreds of thousands, if not millions of views.

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UNIDENTIFIED MAN: It's a very nice elevator.

ULABY: Kevin Allocca says videos like these provide unconventional cognitive thrills and can help infer more information about the workings of people's brains. Our future may be one where entertainment follows less traditional logic but might be bizarrely more gratifying. Neda Ulaby, NPR News. Transcript provided by NPR, Copyright NPR.